text:
Which way (if at all) do the ailerons need to be deflected in a full-rudder sideslip in a Cessna 152 or 172?
Do you typically have to maintain an aileron deflection in a constant-heading full-rudder sideslip in a Cessna 152 or 172? If so, in which direction?  And why -- what is the source of the roll torque that needs to be countered>
Note that aileron deflection is not the same thing as bank angle.

Yes. If you apply full rudder with no aileron, you initially just get a flat skid, but then differential lift starts to have an effect and the inside wing drops because that wing has slowed down, the fuselage is obstructing some of the flow on that side, and if there is wing dihedral, it creates a geometric angle of attack differential. One or more of these factors generate the rolling torque.  It's called "roll/yaw couple".
Some airplanes roll with rudder-only input stronger than others.  On swept wing airplanes the effect is intensely magnified due to the wing sweep and they roll really hard once the yaw angle exceeds 10 or 20 degrees.  Pilots doing jet type ratings discover this right away on their first V1 cut (engine failure) on take off when they don't correct the yaw from asymmetric thrust fast enough and it's taking full aileron just to keep from flipping over.  Side slips are generally not done in swept wing airplanes except in some extreme circumstance.
So the amount of opposite aileron to maintain a constant heading side slip is a function of how strong the airplane's roll/yaw couple is.  A 172 or 152's roll/yaw couple is moderate and you will need some opposite aileron just to keep the wings level.  Plus, to prevent a skidding turn, the amount of aileron has to be more than the minimum required to keep the wings level because some opposite bank is also required to keep the heading constant or else the skid itself starts to pull the nose around. So you end up with quite a lot of aileron in, maybe one third to one half of the available travel, with the wing banked perhaps 10 to 20 degrees, to keep from turning.
There is a lot of variation from airplane type to airplane type and on some the roll/yaw couple is quite weak and it takes only light aileron inputs to hold heading in a skid.  On any airplane you are flying for the first time, this is something you experiment with to find out how strong the roll/yaw couple is and how much counter aileron is required in a side slip.

Nitpicking: 10-20° is a lot, practically extreme. Much smaller angles will cause significant roll. And this is sideslip angle, not yaw (yaw the angle is the same as body heading and is measured from north).

Well, the motion to get to the sideslip angle is still a yaw motion in this case, rotation about the yaw axis, as opposed to sideslip generated by bank.  Yes you get really high roll rates from just a couple degrees of sideslip with swept wings.  You can control a jet quite nicely in roll with little squeezes of rudder.  My point is 10 to 20 of degrees of sideslip angle will cause a moderate roll in a straight wing airplane but will flip a jet on its back.

I know you know, but you explicitly said "yaw angle exceeds...", which is technically wrong. Yaw angle can easily be 180°. No matter how achieved: bank, gust or rudder input (i.e. whether by yaw motion or not), it is the sideslip angle that matters here.

Say you are sideslipping so you have a clear view of the runway thru the pilot side window. You turn the yoke left, so left aileron up/right aileron down, that would start a left banked turn. Then you kick in right rudder to force the tail to move left and counter the left turn of the ailerons.  I do that all the time in my 177, it's a fun way to lose some altitude quick when you realize you're too high on final and don't want to float way down a short runway.
The amount of sideslip that results will depend on how much aileron and how much rudder is used.
Amount of aileroninput depends on the amount of slip desired. Straighten the ailerons and rudder and the plane straightens out. So yes, it must be maintained.

Thank you for answering.  You might be able to expand your anwer just a bit more.  The question has more to do with what aileron input has to be held once the slip is fully established, than what aileron input is need to roll the plane to the necessary bank angle.  PS It may be the case that I have a pretty good idea as to how I would answer this question myself but am interested in how other people would explain the situation.

It may be possible in a turning half circle to dump some altitude with ailerons, but holding it might generate too much of a change in relative wind (sink).  Birds commonly rock back and forth to lose height.  Coordinated S turns also work, especially if it is an engine out approach.  The forward slip recovery is "flat", seems easier.

So are you saying that holding a constant aileron input is not consistent with a constant-heading full-rudder-deflection sideslip?

The rudder is constant (on the 172).  With throttle idle and pitch trimmed to 65 knots, the only thing left to do is work the ailerons, so as needed to hold heading.

Yes, as needed to holding.  And in smooth air with no sudden gusts trying to lift one wing, what will be needed?

PS holding a constant rudder input and working the ailerons as needed to stay on the runway centerline is exactly what I do when landing a rc model airplane in a crosswind. Heading does not stay exactly constant, but close enough to avoid a groundloop. Sitting in the real thing, staying on exactly on centerline and exactly on heading tends to require simultaneous inputs of rudder and aileron.  But to simplify, in smooth air,no need for corrections,what aileron input will be needed to maintain constant-heading slip?

This may be helpful to keep in mind: there is no conflict whatsoever between these two statements: A) "One way to execute a sideslipping approach is to maintain constant rudder pressure and adjust the ailerons as needed for course corrections-- and sometimes the ailerons may be briefly deflected in the SAME direction as the rudder as the aircraft is banked/ turned back onto the desired course-

and B) in the same aircraft, when the rudder is deflected, the dihedral wing geometry, high wing configuration, sweep, etc generate a roll torque in the "downwind" direction, i.e.in the same direction as the yaw string deflects, i.e. opposite to the direction that the slip-skid ball is displaced, i.e. to the opposite direction that the rudder is deflected.  This roll torque must be opposed with an aileron input opposite to the rudder input if net roll torque is to be zero.

Comments have referenced a technique involving holding a constant rudder input and working the ailerons as needed to stay on heading or on course.
Holding a constant rudder input and working the ailerons as needed to stay on the runway centerline is EXACTLY what I often do when landing a rc model airplane in a crosswind. Heading does not stay exactly constant, but close enough to avoid a groundloop. The ailerons are generally deflected against the rudder, but sometimes they may be briefly deflected in the same direction as the rudder during a major course correction involving a large reduction in bank angle or even at times a brief shallow bank in the SAME direction as the rudder is deflected.
Sitting in the real thing, making corrections in turbulent air to stay exactly on centerline and exactly on heading tends to require simultaneous changes in the deflection of the rudder and the deflection of the ailerons.  If the controls are worked in together in a smooth manner to make corrections early, it will be rare that the position of the controls will have to modified so much (from their AVERAGE position during the slip) that the ailerons will ever be deflected in the SAME direction as the rudder.  Certainly the aircraft will never be allowed to get so off course that it will be necessary to actually bank it in the SAME direction as the rudder is deflected to straighten things out.
So back to basics-- in smooth air, with no need for corrections, what aileron input will be needed to maintain constant-heading slip?  That is what the question intended to ask and my answer is that an aileron input AGAINST the rudder input will be required.
This may be helpful to keep in mind: there is no conflict whatsoever between these three statements:
A) One way (not necessarily the best way) to execute a sideslipping approach is to maintain a constant rudder deflection and adjust the ailerons as needed for course corrections-- and sometimes the ailerons may be briefly deflected in the SAME direction as the rudder as the aircraft is banked/ turned back onto the desired course via a reduction in the average bank angle being maintained during the slip.
B) In the same aircraft, when the rudder is deflected, the dihedral wing geometry, high wing configuration, sweep, etc generate a roll torque in the "downwind" direction, i.e. in the same direction as the yaw string deflects, i.e. opposite to the direction that the slip-skid ball is displaced, i.e. opposite to the direction that the rudder is deflected. This roll torque must be opposed with an aileron input opposite to the rudder input if net roll torque is to be zero.
C) During a course correction during a sideslip, a pilot might perceive that he is temporarily deflecting the ailerons in the SAME direction as the rudder is deflected, when he is actually just bringing the ailerons closer to centered to allow the aircraft to roll toward a shallower bank angle.

Appreciate the continuing work on this issue!  Let's not forget one more aerodynamic force that will require a "cross controlled" aileron input.  This will be a sideways drift caused by the relative wind striking the angled fuselage, wing, tail, landing gear of the aircraft, like wind into a sail.  With the 172, this may be a significant portion of the aileron input.  You've made your own cross wind, and correct with ailerons.  Also important is with throttle idle, the sideways drift will be less.  One for the test pilots to check.

What you refer to as "sideways drift", I would call "sideforce".  I would say it is the fundamental reason that the aircraft must be banked to hold heading while the rudder is deflected.  Theoretically, a flying-wing aircraft with virtually no side area exposed to the airflow, could fly a constant-heading strongly-yawed (slipping) approach, to align the landing gear with the runway in a strong crosswind, with virtually ZERO bank angle.  (In such a case, yaw/slip could be induced by a rudder on a very skinny tail boom, or by airbrakes that opened on one wingtip only.)

And note that in the flying-wing case, to hold that near-zero bank angle, a strong aileron (elevon) deflection in the "upwind" direction might still be required, if the wing has dihedral or sweep.  And conversely an aircraft with a flat (no dihedral) mid-mounted wing, and fuselage that has lots of side area, might need lots of bank to hold the heading constant during a full-rudder sideslip, yet little or no aileron input might be needed to maintain this bank angle. (Some r.c. model airplanes intended for "3D aerobatics" fit this description.)

Xtra 300 might be one of them!

To answer your first question briefly:
I asked a friend who flies a C172, he says that he needs a lot of aileron in the opposite direction of the rudder deflection. But he also mentioned that you don't need to slip the cessna, if you put flaps to full you have more drag than you need.
The reason why the aircraft wants to roll in a side slip has several causes, one is that the vertical stabilizer is above the center of gravity and even with the rudder deflected (which would counter the roll) it creates quite a bit of torque. If you do a sideslip and then apply full rudder against the sideslip you are going to roll further because the v-stab then creates even more lift and even more torque to roll the aircraft.
Other factors are the fuselage blocking inflow of the trailing wing,
the wing dihedral that causes leading wing to have a higher angle of attack,
the slipstream of the propeller hitting only one wing and at idle it usually just causes turbulent flow and could disturb the trailing wing flow more which causes a loss of lift,
the lift tends to wash towards the trailing portions of a wing (e.g. in swept wings you have a higher lift coefficient towards the wing tips),
the fuselage shape plays a roll, and I can probably think of another 5 reasons.
This all depends greatly on the aircraft design. Even the wing struts could have an affect here.

I forgot to mention spoilers!

This maneuver, with constant heading and increased rate of descent to correct a high glide slope, is known as a "forward slip".
First, before attempting, speak with a qualified instructor familiar with the specific type of plane you are flying.
Second, practice cross controlled stalls at altitude to validate safe approach speed for that maneuver.  The 172 is extremely forgiving, but this must not be done at marginally low approach speeds (if you are high, you will rarely be slow, I did mine at 65 knots).
Thirdly, be mindful that the POH does not recommend trying this at 30 degrees of flaps as a tail pitch oscillation will result, due to flap and slip induced turbulence on your tail.
With the 172, roll coupling with rudder is much less than at cruise speed, so:
You are coming in at 65 knots (trimmed), 20 degrees of flaps, throttle at idle, and looks like it will be past the first 1/3 of the runway, decision:   1.  Go around  2. forward slip
If you are not too high and elect to do a forward slip in a 172, push the rudder all the way over.  This would probably be lethal in a low wing, dihedral aircraft due to roll coupling, but the 172 yaws with much less roll.
You will be seeing your old aiming point moving up on your windscreen.  The aileron is used to hold line with the runway, you just work it back and forth.  Once your (shorter) aiming point is achieved, smoothly center ailerons and rudder first, then use pitch to break glide path and round out for flare and landing.
You should not need to stay cross controlled while applying elevator.
As far as how much aileron is needed in the maneuver,  I do not recall it being close to what was available in either direction.
We want to SAFELY increase our rate of descent. Why full rudder deflection? To maximize drag while maintaining safe speed and AOA. Ailerons are used to counter the drifting and rolling tendency created by side force. This is a FORWARD SLIP. It could also be called a "flat or skid" slip. It works.
Now to consider the SIDE SLIP. Rather than increasing drag, we reduce VERTICAL lift component by rolling with ailerons. This can be done very gently to coax a plane floating in ground effect down to the runway.
Recovery from the forward slip uses the rudder, which is always functional, even when the wing is stalled.

"Second, practice cross controlled stalls at altitude to validate safe approach speed for that maneuver."  -- So it IS in fact a cross-controlled maneuver?  I.e. the ailerons ARE in fact deflected, if the heading is constant?

Absolutely, yes.

But-- you said before that there was little or no slip-roll coupling in a Cessna 152 or 172.  I'm sorry Robert I think I had better break this off.  Comments are not intended for this anyway.

No problem, just very little.  When I went from RC  to full scale, one of the first things I did was push the rudder on the 172 and see what it did. Hardly anything!  Very flat skid.  There is some, you mentioned doing rudder turns back and forth, but the roll really needs to be helped with the ailerons, the plane is designed to self correct hands off, and to be turned coordinated.

Related-- https://aviation.stackexchange.com/questions/48919/how-to-handle-vacuum-and-turn-coordinator-failure-in-imc/56133#56133 .I was actually stretching the truth a little to say that I saw a video of this.  Yes I saw the video, but I also filmed the video.  Slip-roll coupling in Cessna 120, 150, 152, 172 is NOT trivial and is generated primarily by the high-wing configuration.  Of this bunch I think the Cessna 172 has the most dihedral; the rest have very little. I''ve also done reversing turns though at least 35 dgrs bnk, usng the rdder pedals only, hands-off the yoke, in all these a/c.

With cross control ailerons are applied in the opposite direction, but there did not seem to be a major difference into or away from rudder to control direction.  It will vary from one type of aircraft to another,  Personally, I just wish they could give us more than 3 flap settings!

Believe me, it will couple a lot more on a low wing.  There is nothing aerodynamicly below the CG to counter the dihedral effect of the wing (and the tail) It just goes right over, weight on top just happy to go along.  So, more properly, there is relatively little.

No, I don't believe you.  I think we have another question for Aviation Stack Exchange in the making here.  Are you going to ask it or am I?

Well, I can only ask is you can go farther than 35 degrees?  A low wing will be through 2 rolls before you do.  Note aircraft evolution from biplanes, to high wings (1920s) to low wing dihedral (WW2).  They needed faster roll rates.  The 172 is more like a hang glider in comparison.  I call them hang planes.  But thanks for the discussion,

Of course the low wing a/c are said to have faster roll rates.  The tendency through at least WW2 was to evaluate roll rate in the case where the pilot did NOT give a coordinating rudder input as he moved the stick to initiate the roll.  A roll input w/ no "coordinating" rudder input always creates adverse yaw, and this will interact with "positive effective dihedral" due to actual dihedral, sweep, and/or high wing placement to generate a roll torque component AGAINST the intended direction of roll,

(Ctd)   For a similar actual dihedral angle, the high-wing plane will always have the greater "effective dihedral" and thus the lower roll rate, if the pilot is not making an adequate "coordinating" rudder input along with the stick input.

And now this is probably a good time to "avoid exteneded discussions in comments".

Well there you go!  Roll stability "effective dihedral" vs "dihedral effect" from side slip.  More tomorrow!

At my home field, it's common for App/Twr to request "best speed" due to following jets, and that means crossing the fence high and at 100kt+. A short (but hard) forward slip in the 172 and I'm touching the numbers at 65kt. Easy peasy. I almost needed to change my pants the first time my CFI showed me, though; the view is terrifying when you're that close to the ground and not expecting it.

Robert, you actually use roll to get settle out of ground effect?  That isn't something I would recommend...

@Michael Hall dipping a wing very slightly can be done, it is not standard but it works. Not recommended close to stall though.  Keep in mind it is routinely done in a crosswind landing (with opposite rudder), so not a big sin, provided airspeed is adequate.

Fair enough, I have touched down on one wheel plenty of times.  Intentionally, and unintentionally!  One thing to clarify though, aerodynamically there is no difference between a "forward" slip and a "side" slip.  The plane knows only that it is slipping into the relative wind.  In fact I really don't recall people distinguishing them as separately as we do on this forum.  I just don't want to confuse any neophytes.

And finally, I would only practice cross controlled stalls if I also planned on entering a spin and practicing recovery.

@Michael Hall My experience was in a 172.  The applications are different, as are the techniques.  In a 172, because of its incredibly forgiving design, one could fully deflect the rudder in a forward slip and still have adequate directional control with ailerons.  In a side slip, only enough aileron was applied to hold the line against crosswind,  and only enough rudder to point nose straight. Close cousins though.  With the 172, practice at altitude showed it to be extremely tolerant of cross controlled flight at 65 knots, and spin prevention at stall was easily controlled with rudder.

Yes, but other aircraft are not as forgiving.  Recommending that someone practice cross controlled stalls without addressing the spin risk is not good...


text:
In the US, can airspace simultaneously be E2 and E4? What happens at KSTC to the airspace in the dashed magenta boundary when the tower closes?
In the US, can the same airspace simultaneously be E2 and E4?
Consider the case of KSTC -- St. Cloud Regional Airport, MN.
http://vfrmap.com/?type=vfrc&lat=45.546&lon=-94.059&zoom=10
On page E-178 of the FAA's "Airspace Designations and Reporting Points" document, also known as "Joint Order 7400.11C", https://www.faa.gov/documentLibrary/media/Order/JO_7400.11C.pdf, we find the definition of the E4 airspace at KSTC.  This definition clearly corresponds to the airspace that lies within the dashed magenta border but outside the dashed blue circle.  No note is given to indicate that the effective hours are less than 24/7.
On page D-41 of the same document we find the definition of the Class D airspace at KSTC-- this is clearly the airspace in the dashed blue circle, up to 3500' MSL, and there is a note to see the Airport/ Facilities Directory for the effective hours of operation.
On page E-54 of the same document we find the definition of the E2 airspace at KSTC-- this is clearly written to include all the airspace in the dashed blue circle (but with no altitude ceiling) AND all the airspace within the dashed magenta line.  Again there is a note to see the Airport/ Facilities Directory for the effective hours of operation.
Here is the actual description of the E2 airspace from page E-54 of JO 7400.11C:
"AGL MN E2 St. Cloud, MN
Within a 4.1-mile radius of St. Cloud Regional Airport and within 2.4 miles each side of the St. Cloud VOR/DME 143° radial, extending from the 4.1-mile radius to 7.2 miles southeast airport. This Class E airspace area is effective during the specific dates and times established by a Notice to Airmen. The effective date and time will thereafter be continuously published in the Airport/Facility Directory.''"
In most cases of airports with part-time control towers where we have a dashed magenta E4 "extensions" like this, IF when the tower closes the Class D airspace reverts to E2 rather than G (which is also possible), one of the following two situations will apply:
1) The part-time E2 airspace is defined to ONLY include the airspace in the dashed blue circle, while the E4 airspace is implied to be in effect 24/7.  This is the norm-- it is by far the most common situation, nation-wide.
or
2) The part-time E2 airspace is defined to also include the airspace in the dashed magenta borders, but there is also a note in the E4 airspace definition to see the A/FD for the effective hours of operation of the E4 airspace, presumably implying that when the E2 description is active, then the E4 description is not.  This situation is much less common over the nation as a whole, but for some reason it is fairly common in the northeastern US.  Example: KLNS, and about a dozen other airports.
But neither of these descriptions apply the airspace at KSTC.
Three other airports with airspace definitions set up just like KSTC are KRST, KILN, and KRAP.
At these 4 airports,
1) Is the lack of reference in JO 7400.11C to limited effective hours of the E4 airspace simply an oversight?  I.e. a mistake?
or
2) In such a case is it always simply assumed that the "lower" airspace class (E4) simply is superseded by the "higher" airspace class (E2) -- similar to what is presumably considered to happen when E2, E4, or any other kind of Class E airspace, which usually has no specific defined upper limit, hits the floor of the Class A airspace high above?  If this is the case, then why at KLNS and about a dozen other airports where the E2 is configured like at KSTC, do we find (in JO 7400.11C) that a note to see the A/FD for the effective hours is included in the description of the E4 airspace, as well as the descriptions of the E2 airspace and the D airspace?   If this note is not really needed -- if the E4 effective hours are automatically limited simply by virtue of the fact that the E4 airspace is superseded by the E2 airspace whenever the E2 airspace is effective-- then why include this note in the E4 airspace descriptions for KLNS and other airports?  At the very least we have an inconsistency here.
or
3) Is the airspace in question considered to both E2 AND E4 airspace during the hours that E2 airspace is in effect (i.e. when the tower is closed)?  I know of no specific FAR whose meaning would be confused or obscured if this were considered to be true.
Many FARs appear to apply specifically to E2 airspace-- relating to SVFR operation, aerobatic flight, ultralight flight, recreational and non-recreational sUAS operation (commercial and hobbyist "drones", model airplanes, etc), and even unmanned free balloon flight-- for more see this related question -- but the interpretation of those FARs would not necessarily be confused if the airspace were also considered to be E4 airspace at the same time.
Naturally, the Class E visibility and cloud clearance requirements for VFR flight apply to both E2 and E4 airspace, so there is no problem there.
Question A: Which of the three possibilities listed above is the most accurate description of the situation at KSTC, KRST, KILN, and KRAP, and why?  Or is it simply ambiguous as to which is the case?
(It's not clear that the answer to question A would make any operational difference at these 4 airports.  However it could have some bearing on the interpretation of the airspace designations at some other airports.)
Question B: Also, more generally, in the US, would it ever be permissible for the same airspace to simultaneously be considered to be E2 airspace and E4 airspace?

Comments are not for extended discussion; this conversation has been moved to chat.

Since I worked the airspace around KRAP, I'll cover that scenario for you. The tower at KRAP closes at 10 PM local, and the airspace at the field reverts to E2. The TRACON at KRCA closes at the same time, so Denver Center (that would've been me) gets the airspace after hours.
We treat all Class E airspace near an airport the same, so the closest of your answers for the first question would be 3.
There's confusion, however, as to whether a Special VFR can enter those extended areas when requesting entry/exit/transiting the surface area. My answer is YES, because that airspace will be protected. I will not authorize any IFR or other SVFR operation in that area, if I have given you a clearance. To do so would be an error on my part. This does not keep me from holding aircraft near the field (at HELTA)if necessary, but they will be clear of your aircraft by altitude restriction. Remember, this is the Center environment. A terminal environment may have additional restrictions placed on them, simply because they work many aircraft in a small and congested area.
As far as your second question goes, NO, the designations for individual areas within the same class would not change, but I'll still protect those areas for your flight.

Thanks for the answer.  FYI,  a few months ago I sat on on a zoom conference where several high-level FAA staffers offered conflicting opinions on whether or not the language in the FARs describing where sVFR operations may be authorized, and where VFR flight without a sVFR authorization is prohibited under certain conditions (e.g. below a 1000' ceiling), did or did not apply to "extensions", i.e. E4 airspace.

(ctd) One of them said something to the effect of "pilot checkrides have been failed because of the ongoing confusion over this issue; it's been unclear ever since the 1993 "alphabet" airspace re-organization".

You got that right.

quiet flyer, I teach new controllers the same way I stated. My interpretation is simple, it's easy to remember, and it's safer. I don't know, without specifics, whether a SVFR would transition an extension on their way into or out of Class E (and why shouldn't they), but if I protect the airspace, it doesn't matter. I've never had anyone in the FAA argue against this interpretation once  I explain the safety concern.

Before the alphabet soup designations, Class E surface areas were called "Control Zones", and the extensions were part of the zone for an airport. There was no border or distinction between them.

yes, I do understand that.  And one could possibly argue that if the FAA intended the conversion to Class-E surface areas, some of which were "extensions" and others of which actually contained the airports whose approaches they were protecting, to cause significant changes in the application of certain FARs, then that SHOULD have been addressed in the various NPRMs etc accompanying the rule-making process around the conversion to the "alphabet" airspace classes.  But the rule-making process was rather complex, with several different rounds of NPRMs, (ctd)

(ctd) so it's not really a decisive argument.  The second half of this answer https://aviation.stackexchange.com/a/75022/34686 goes through several issuances from the FAA that indicate that surface-level Class E "extensions" should be treated differently from surface-level Class E airspaces that are not "extensions", in relation to the application of several different FARs.

(Ctd)  By the way, in relation to https://aviation.stackexchange.com/a/75022/34686, that answer is long overdue for a revision.  Among other things, I intend to remove some of the content near the end,  starting with "The present question goes on to ask:
And which is the better interpretation of the language of the Federal Aviation Regulations...?"  Basically I think the language in the FARs and supporting documents is just too poorly-written and ambiguous to decisively support one interpretation over the other-- and should be fixed.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
What is causing these "corners" on this F-104 V-n diagram?

In this V-n diagram for an F-104 (source: this Wikipedia link), on the left-hand edge of the flight envelope, what is causing the "corners" that we see at the following points? (Numbers are approximate)
30,000', 375 knots IAS, and 5 G
40,000', 295 knots IAS, and 3.1 G
50,000', 230 knots IAS, and 2 G
60,000', 180 knots IAS, and 1.25 G
70,000', 140 knots IAS, and 0.95 G
Do these points simply represent the "corners" of what performance is possible while still maintaining horizontal flight at a constant airspeed (i.e. while maintaining both altitude and airspeed), and if more engine thrust were available, these "corners" would move higher up and to the right, continuing to follow the stall speed curves?  I.e., do the actual stall speed curves continue upward from the corners following a path that is more or less continuous with the lines below the corners?
(Note-- re the last data point--  a G-loading of less than 1 is obviously incompatible with constant-altitude flight-- but the data point still could have mathematical or theoretical significance -- e.g., if the aircraft weight decreased by 5%, then the aircraft could maintain constant altitude.)
Wouldn't it be theoretically possible for a pilot to operate well outside the illustrated envelope, say, by pulling 4G at 340 knots IAS at 40,000'?  Am I correct to assume that this could be done without stalling the aircraft, but the aircraft would be losing either altitude or airspeed continually?  Because it is on the "back side" of the thrust-required curve?  Whereas that would not be the case for a point further to the right, on the other side of the illustrated curve?
If the actual stall speed curves do in fact continue more or less smoothly upward from the "corners", this would imply that if, theoretically, we were setting a "maneuvering speed" to protect the aircraft from exceeding 6G's, it would need to be at about 430 knots IAS at 20,000' (the "cornering speed" shown on the diagram), but it would need to drop to about 380 knots IAS at 30,000' -- well outside the envelope of the figure as drawn.  Is this in fact the actual situation?
Is this particular diagram really as much about achievable performance as about protecting the aircraft from excess loading, at least in the positive-G part of the flight envelope?
Is it therefore not strictly accurate to call this particular diagram a "V-n diagram"?
Related ASE questions and answers--
(Q): In this F-104 V-n diagram, why does the stall speed (in terms of IAS) decrease with altitude in some parts of the flight envelope?

https://www.boldmethod.com/learn-to-fly/aerodynamics/coffin-corner-where-vne-and-mmo-meet/

@ymb1 -- lots of tags deleted there (edit #12), was that all really necessary? Especially as the thrust of this question was that the answer might in fact have a great deal to do with aircraft performance.  And physics is a pretty broad brush that would seem to include this question.

@Vikki-formerlySean -- the problem with including that last "corner" is that it plays havoc with my question "Do these points simply represent the "corners" of what performance is possible while still maintaining horizontal flight at a constant airspeed".  Obviously horizontal flight cannot be sustained at less than 1.0 G.  Therefore I will modify back to something closer to a previous edit that removed that "corner".

@quietflyer: The problem with not including the last corner is that its existence invalidates your proposed reasoning for the corners - given that horizontal flight cannot be sustained at less than +1 G, the presence of a corner at less than 1 G means that those points cannot possibly be "the 'corners' of what performance is possible while still maintaining horizontal flight at a constant airspeed".

@Vikki-formerlySean -- ok, thinking it over, stand by for another edit

@Vikki-formerlySean -- (done) -- but I've had a significant change of perspective-- see my most recent comments under Peter Kampf answer -- and see also related question https://aviation.stackexchange.com/questions/86617/in-this-f-104-v-n-diagram-why-does-the-stall-speed-in-terms-of-ias-decrease-w

what is causing the "corners" that we see at the following points?

Compressibility. Close to Mach 1 the lift curve slope increases according to the Prandtl-Glauert rule with the factor $\frac{1}{\sqrt{1-Ma^2}}$. Since the X-axis shows indicated speed, the Mach 1 point moves left with increasing altitude. Technically, those corners should also be added for the negative lift limit.

Do these points simply represent the "corners" of what performance is possible while still maintaining horizontal flight?

No. A v-n-diagram covers the whole load factor range while horizontal, steady flight happens along the line y = 1g (except for turns or inverted flight, of course). Adding more thrust will not change the limits. Maneuvering is only possible/permitted (see below) inside the lines and maneuvering  at constant altitude depends on thrust which is not included here. The lines show lift and structural limits; thrust envelopes look different.

Wouldn't it be theoretically possible for a pilot to operate well outside this envelope?

Not really. Momentarily yes, for example the stall lift coefficient moves up with higher pitch rate, but that only works while pitch angle is increasing. Also, at supersonic speed (after all, your example of 340 KIAS @ 40 kft is equivalent to Mach 1.07) the envelope is limited by angle of attack, not lift. Therefore, 4g at Mach 1.07 in 40 kft is outside of the permissible flight envelope but may be reached if the pilot overrides stick shaker and stick pusher (depending on control authority).

So this diagram is really as much about achievable performance as about protecting the aircraft from excess loading?

Yes. The region left of the stall lines is impossible to fly since lift is limited at lower speed. However, the top speed limit might well be exceeded in a dive if the pilot chooses to do so. Equally, the g limit might be exceeded right of the point where the envelope becomes horizontal.
Thank you @JanHudec for pointing out correctly that those areas which can physically be reached by improper flying but might incur damage to the airframe are colored red.

Comments are not for extended discussion; this conversation has been moved to chat.

For the last point, you could note that the structural limits—where you can get by mishandling the plane, but risk damaging it—are marked with red on the diagram.

The answer still could be improved by modifying the statement  "horizontal flight happens along the line y = 1g."

@quietflyer You are right, in turns the load factor is greater than 1. When I wrote this I was only thinking of loops.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Which is the airliner with the most passengers per lavatory?
When flying long distances in large airliners like the B777 or the A380, there always seem to be long queues in front of the lavatories, generating longer waiting times than in the past. Kinda looks as if there are fewer and fewer toilets per passenger on board.
Are modern aircraft designed with fewer lavatories per passenger on board? Which is the airliner (CFR 14 Part 25) still flying with the most passengers per toilet?

Most small planes have no toilets, so the ratio is infinity.

Here's an astonishingly long discussion about this very topic, including actual airplane examples: https://blog.thetravelinsider.info/2012/11/how-many-restrooms-are-enough-on-a-plane.html

@Greg Hewgill - +1 - great info

This is not necessarily an attempt to answer your question directly. But I do have some interesting information.
I use to be the night shift supervisor for Continental Airlines in Anchorage Alaska from 1998 to 2005. We primarily serviced B757 and B737 flights from Newark NJ or Houston TX via Portland or Seattle each day (4 winter, 6 summer flights). About half the flights had lavatory problems.
The MEL (minimum equipment list) only required the lavatory closest to the cockpit to be operational for a flight. We averaged about 190 pax (max was 230-290). Imagine a B757 with 200 passengers with only one lavatory for a 5hr flight between NJ and WA (WA to AK was 3hrs) - how inhumane! And I did rarely see flights with only two toilets that worked (never one).
This was an eye opener to me that the FAA (govt) is not looking after the best interest of the public. I could tell you other bone chilling experiences but this is not the proper place or time :(
So with due respect, I am warning that there is a difference between the number of toilets in an airplane, and the number of toilets that actually work!

@jjack The fact they are closer to the ceiling is not important, if not in fact advantageous. The fact that they are not held by their seatbelts is a problem.

@jjack - +1 - Your health concerns are well founded for this and other problems - for example blood clotting.
see: http://www.clotconnect.org/about-clot-connect/news/be-clot-aware-when-traveling

@jjack +1 good questions and I just don't know... but clear air turbulence no longer seems (and I could be wrong)  to be a problem. While there are injuries from time to time because pax are not wearing seat belts during cruise, I do not recall any deaths or aircraft crashing from clear air turbulence in the last 30 years. Great to hear from you - in this and other discussions...

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

authors: Vladimir F Героям слава


text:
Cross Country flight: what do I have to consider concerning radio communications?
I'm tasked with developing part of a cross country flight plan to cap off my ground school class. Among my group, I am handling the radio communications and regulations. However, I was not provided further details, and came here to gain a greater understanding of what I need to accomplish. Specifically, the trip is to fly from Aspen, fly by Capital Peak for the view, and then land in DIA (KBDU-KASE-KDEN).
As far a radio communications go, I imagine I need the frequency of each of the listed airports, but is there anything else I need to consider?
Edit: Further Information:
I'm flying N370SP, a Cessna 172S Skyhawk SP. I pick up friends (190, #320) and luggage (35, #60).

Hi.  Welcome to SE.Aviation.  Why weren't these requirements covered in the class?  Are you being asked to consider regulations which you do not yet know exist?  As to your question, it's doing OK until that last paragraph where it gets very broad.  I can think of half a dozen questions I'd need to ask before attempting to answer your multiple questions.  As it is, it's likely to get closed as "too broad".  Are you able to make it more concrete?

Welcome to Aviation.SE. I took the liberty of limiting the scope of your question to one topic, otherwise it would be too broad and closed. It would help if you could specify which kind of flight/aircraft you plan to (simulate to) use: IFR/VFR flight, small aircraft or commercial airliner.

what do 190, #320 and 35, #60 are supposed to mean?

Thanks @Federico, you're right it was too broad before. I've edited the the post to include more information as well. And regarding those numbers, I'm uncertain, and was hoping y'all would have some insight. My instinct is that they denote location from center of gravity and weight of object.

@Federico I think those are weights

Weights and moments have nothing to do with radio communications

Thank you for the tail number. I'll track your flight, and listen to the available frequencies on LIVEATC. Then I'll tell you how you did. Heh.

A common way to approach this is to walk through the flight and write down each frequency you'll need in order. Your route is a bit unclear (are you departing Aspen or landing there?) but let's say it's KBDU-KASE-KDEN and it's a VFR flight. And I'm assuming you're only asking about comms, not nav.
You think through what you're doing at each point and then write down the station, frequency and what you plan to say, request or listen for, as the case may be. For example, you're departing KBDU; it's uncontrolled so you'll check the AWOS and then use the CTAF to announce your intentions as you taxi and depart.
After that the route to KASE seems to be through uncontrolled airspace but you'll probably want to get the Empire and Copper Mtn AWOS along the way. And if you want flight following then you'll have to call Denver Center to get it.
KASE is controlled, so you'll need to get their ATIS, then call the tower, and after landing you'll be handed off to Ground. Departing KASE, you'll get the ATIS, call Ground, then the Tower and after departure maybe Denver Center again for flight following.
And so on...
You'll end up with a frequency log like this:

KBDU - AWOS - 118.825 - Get altimeter, wind, etc.
KBDU - CTAF - 122.725 - Announce taxi and departure
Denver Ctr - 126.1 - Request flight following
Empire AWOS - 134.325 - Get WX and compare to forecast; change flight plan if needed
[...]
KASE - ATIS - 120.4 - Get WX and runway in use
KASE - Tower - 118.85 - Announce landing intentions (check two way comms before entering class D!)
KASE - Ground -121.9 - Request taxi to FBO
[Etc...]

This can be a really useful planning exercise, especially in unfamiliar areas. If you're unsure of the phraseology or procedures for any item on the list then you can talk to your instructor about it, and listen to real comms on LiveATC. KDEN in particular would (will?) be busy, it's class B.
But remember that plans change. ATC may give you an unexpected frequency, or you may copy down a frequency incorrectly and then find no one is listening. Make sure that you update your log in flight as needed; don't fixate on it being 'correct' to the point where you ignore instructions or information to the contrary; and be able to look up frequencies quickly on your charts or flight software.

Yes, DEN will be very busy. It's the 6th busiest airport in the world by movements (5th in the U.S., behind only LAX, DFW, ATL, and ORD.)

A note on Class D (at KASE in your answer): no clearance is required to enter, only two way radio communication (tower doesn't even need to acknowledge your call-sign—unlike for Class C). Tower will not usually say anything like "cleared into the Delta", and it should not generally be expected. The only time you would need to be "cleared" into the delta is if tower had previously instructed to remain clear. Class B is the only non-special–use–airspace that requires an explicit clearance to enter.

@JonathanWalters Good catch! I've reworded that part. By the way, the AIM 3-2-5 says that the tower must acknowledge your callsign before you can enter, that's the same for C and D: "It is important to understand that if the controller responds
to the initial radio call without using the aircraft callsign,
radio communications have not been established and the
pilot may not enter the Class D airspace"

You are correct. I was mistaken on that point. It's good to brush up on these things after all these years.

@Pondlife When making contact with a class d tower, if they don't have any specific instructions for you, what would be the usual reply from atc? On the class b I will hear them say "N1234 radar contact." Would it be the same st class d?

@TomMcW Class D is pretty small so they usually give me their instructions for joining the pattern immediately. If I'm just passing through their airspace then they usually say "Roger, local altimeter is 2992" or something similar.

There are three categories of radio communication to deal for each leg of a flight:

arrival and departure airport: tower/CTAF, ATIS/ASOS/AWOS, Ground/Clearance Delivery
En route ATC: arrival/departure, center
En route weather and information: Flight Service, Flightwatch, HIWAS, en-route ATIS

You have to decide which of these services you will interact with, and know where to find the frequencies (almost always a chart or the A/FD) and how to contact each of them.

Depending on what exactly is meant by "radios", the student may also be responsible for tuning, identifying and following VORs or other radio based nav-aids.

very true. i read radio communications as voice.

Normally what you do is group information for each leg of the flight. Each bundle of information should have everything you need, not just frequencies. So, you should have field elevation, runway length, etc.
Airports do not have just one frequency as your question seems to imply. Normally you will always have two frequencies at a minimum, which is CTAF and ground. For larger airports you will also have clearance delivery and tower. Make sure you label each frequency, that is critical. You do not want to be trying to get landing clearance from the guy that is driving the fuel truck.
The trickiest thing in radio work is a handover wherever you take off from one airport and enter the airspace of another. Since your radio may only have two frequencies you will have them set to tower and ground of the departure airport, but will need to immediately switch to ATC as soon as you take off while you are trying to do fifteen other things. So, if you have situation like this, you want to plan ahead carefully for how you handle it.
It is good idea to find out which airports have shared CTAF. In some cases you will hear traffic on CTAF which is actually pilots at other airports, not the one you are at. They are supposed to announce the airport always, but do not always do so, also sometimes it is garbled. It can be very confusing if you hear some guy say "on final for one six" and you are looking around and wondering where the hell he is---he is at a different airport. Don't make that mistake.
Finally, practice your comm phrasing as much you can. You want to say exactly the right thing. It needs to be automatic. You don't want to be in a situation where you need to request something and can't remember how to phrase it. Practice your phraseology out loud until you have it down cold.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Can tower clear aircraft for take off with traffic still on the runway?
How much separation is required after an aircraft lands before ATC can clear another aircraft to take off from the same runway? On longer runways are small aircraft allowed to commence take off roll or be cleared for take off while the preceding landing aircraft is still on the runway? I looked and was unable to find any ATC instruction requiring separation between landing and departing traffic on the same runway.
While this would be unsafe, it seems to me that I have been cleared to take off while there was still an aircraft finishing its landing roll. By the time I had lined up for take off the preceding traffic is alway clear but is this still a "legal" practice to be cleared for take off before the preceding air craft calls "clear of the active"

I just found this video were an A380 is landing on a runway from which a B737 has taken off inly few seconds before. Separation in case of go around may be enough but the relative size of both aircraft make the video impressive.

According to the ATC orders controllers can indeed clear an aircraft for takeoff 'early':

3−9−5. ANTICIPATING SEPARATION
Takeoff clearance needs [sic] not be withheld until prescribed separation
  exists if there is a reasonable assurance it will exist when the
  aircraft starts [sic] takeoff roll.

A common scenario would be clearing an aircraft that's holding off the runway to take off while the landing aircraft is still on the runway. If the controller expects that the landing aircraft will be off the runway by the time the holding one turns onto it, then it would be allowed.
Section 3-9-6 lists the conditions for allowing an aircraft to start its takeoff roll. It's too long to quote here and you can read it yourself but the two main  conditions seem to be:

The other aircraft has departed and crossed the runway end or turned to avert any conflict
A preceding landing aircraft is clear of the runway

All references for this answer are in the FAA Order 7110.65.
A departure cannot start their takeoff roll before the previous arrival has cleared the runway. What most controllers will do, is use a provision for anticipated separation (3-9-5), which basically means, if someone's holding short, and you can predict when the arrival will exit, you can go ahead and issue the take-off clearance. The controller will keep an eye on things, and if it looks like it won't work, or something's changed, the pilot of the departure will be told something along the lines of: "[Callsign], cancel takeoff clearance, runway [x] line up and wait, traffic exiting downfield".
Can 2 or more aircraft be on the runway at the same time for the same type of action? Yes, in a few cases.

Between 2 arrivals, during daylight, small single engine propeller driven aircraft, and small twin engine propeller driven aircraft weighing less than 12,500, as long as the lead aircraft is at least 3000, or 4500 feet down the runway, the next can continue and land.
Also departures, depending on type, the as long as separation exists, 3000, 4500, or 6000 feet and airborne between departures is all that's needed under normal situations.

All the full details can be found in Chapter 3, Sections 9, 10 of the 7110.65.

I've received an instruction to "start your roll" when Tower is trying to squeeze departures between closely spaced arrivals; due to separation, they can't issue a takeoff clearance until the previous arrival has turned off the runway, but if they had me line up and wait, I'd be in the way of the next arrival.  This is only practical when the runway is so long that waiting a few extra seconds to put in full power simply doesn't matter.


text:
Is it a flight violation to mishear ATC instructions for exiting the runway?
I was on landing rollout and misheard a tower "turn off at xxx switch ground" call. We read back the incorrect taxi way and turned off there and switched to the ground frequency. After our incorrect read back we were not contacted again until ground told us to call tower. I was under the impression that the landing aircraft had the right of way over any traffic behind them, even on roll out. I was also under the impression that a tower cannot stop you from using the whole runway.
Is missing a directed turn off a runway a flight violation? If so what FAR/AIM or regulation did it violate? Is the fault with us for mishearing or with the controller for not correcting us? Does this count as a runway incursion? Does the controller maintain responsibility for maintaining separation until we taxi clear?
To answer a few of the questions from below:
when we contacted the ground controller, they gave us a phone number to contact tower then gave us a taxi clearance. When they told us to call i became concerned with receiving a flight violation. We were not corrected to my knowledge, we only heard radio traffic once we had turned off the runway. This was also not a LAHS operation.
another question: From the AIM 4-3-20 it says : "the following procedures must be followed..." "exit the runway without delay"
" is that at the discretion of the pilot?
also if tower gives you a taxiway instruction to leave the runway is that an instruction or a clearance?
Is it a good idea to call the local FAA office and see if they have opened an investigation?

Related: JO 7110.65 --- 3−10−9. RUNWAY EXITING (page 158).

Whatever happened exactly, it sounds like it's worth filing an ASRS report right away

After switching to ground did you contact them before taxi? "Switch ground" doesn't sound the same as "monitor ground". I agree with @Pondlife, file an ASRS now.

I think the use of incorrect phraseology by ATC added to this, as is so common, and, if they have spaced traffic behind so close that you turning off at the wrong exit caused a problem, that's ATCs problem again, not yours.  What if you had had to stop on the runway?  You're the PIC, the safety of the aircraft is yours.

About your last edit on calling the FAA or not, I would say definitely not. If they are invesigating they'll contact you, and if they aren't then there is zero benefit (to you) in stirring things up. I would still file the ASRS, though. And see this question

@Andykraven, sorry I see that this is an old one, but I have to ask:  You mention you were given a phone number and asked to call tower.  Did you call later?  What did they say?!  They could either chew you out, or apologize for not catching and correcting your readback.  I am very curious how that conversation went, and surprised nobody else commented or asked about this...

I don't think you violated any regulations. It was an ATC instruction, not an ATC clearance.
It was an instruction you were unable to comply with. The instruction was badly timed and was obviously not clear since you did not correctly understand it.  In the busy time during the landing roll, you understood something different, and read back what you understood it to be.
The landing roll-out can be a busy time needing the attention of both pilots.  ATC issuing an instruction while you are basically still in the landing roll should not be expected to be complied with unless it is happens to be convenient for you to do so.
Many airlines SOP say that you do nothing until you are clear of the runway. Both pilots remain heads up and don't touch anything. The pilot in command alone will decide where it is safe to tun off the runway. If ATC makes a "Request", and it can be safely complied with, then the PIC may decide to deviate from SOP and comply.
If you ran off the side of the runway trying to comply with an ATC "request", who do you think will be held responsible? (I'll give you a hint, it won't be ATC)
This is a prime example of why ATC should not be doing this.

An excellent example of this in a commercial setting: https://www.youtube.com/watch?v=x23fBpxuWGM

I agree. The biggie is that you read back the instructions and were not corrected. As a former ATC, I can tell you the supervisor would probably yank my headset out of the console and take over if I made that mistake :)

Is there any way to tell if they are investigating me? I haven't received any notic yet. How long does that usually take?

Mike has a good answer, but I thought it was worth while mentioning something you say in your question:

...I was also under the impression that a tower cannot stop you from using the whole runway.

While in many cases this is true, there are some that it is not. The main example of this is a Land and Hold Short Operation (LAHSO). If you accept a LAHSO then you are required to comply with the hold short point on the runway and not go beyond that. (The only other one I can think of is when a crossing runway is closed).
So if you had accepted a LAHSO request (and its up to you as the pilot to accept or decline the request), and subsequently used more than the LAHSO permitted you to, this would be a violation.
Also, if you are a light plane and want more than your fair share of runway, its usually "polite" to tell the controller that you want "full length". The controller is trying to space out landing aircraft and may assume that you don't need 8000+ feet of runway in your Cessna 172. Legally unless you accept a LAHSO you are welcome to use all of it, but the controller will be a happier person if you tell them you need more. I do this quite a bit when coming in on a certain runway that has the FBO at the opposite end, its better to land long than spend 10 minutes taxing. The controller may request that you "make it short" for landing aircraft.

To clarify, you can accept a LAHSO and still abort the landing (which will put you beyond the hold short point), and indeed you have to if you botch the landing in such a way that you'd be unable to stop before the hold short point.

@falstro Usually a botched landing results in a go-around, not a full stop. If you accept a LAHSO and go beyond the hold short even with a botched landing you are violating a clearance. LAHSO doesn't mean you can't go around.

Yes, my point exactly; just saying if you go around, you can go past the hold short.

Exiting a runway is purely at the discretion of the PIC. The tower-recommended exit is just that: a recommendation. This is a safety issue. The pilot exits the runway where they and they alone decide it is safe to do so.

Eh... if you're still barreling down the runway at 100+ knots and tower says to turn at the taxiway in 300 feet that's obviously not going to happen. If you're at 20 knots halfway down the runway and tower tells you to take the next exit, and you decide you want to keep on trucking to the end? Pilot deviation. (Assuming all surfaces clear of contaminants, etc.)

The topic is as relevant as it was when it was initially posted. So some notes:

ICAO Annexe 10 extract para 5.2.1.9.2.2 PANS.
An aircraft station should acknowledge receipt of important air
traffic control messages or parts thereof by reading them back and
terminating the readback by its radio call sign.
Note 1.— Air traffic control clearances, instructions and information
requiring readback are specified in PANS-ATM (Doc 4444).
Note 2.— The following example illustrates the application of this
procedure:
(ATC clearance by network station to an aircraft)
Station:   TWA NINE SIX THREE MADRID
Aircraft:   MADRID TWA NINE SIX THREE
Station:   TWA NINE SIX THREE MADRID — ATC CLEARS TWA NINE SIX THREE
TO DESCEND TO NINE THOUSAND FEET
Aircraft (acknowledging):   CLEARED TO DESCEND TO NINE THOUSAND FEET —
TWA NINE SIX THREE
Station (denoting accuracy of readback):   MADRID

I'd say missing an ATC directed turn off the runway, after a correct and confirmed readback, could be a violation, but clearly, this wasn't the case. So no violation, and no intended violation of procedure, but there certainly was an error as you point out yourself.

In the first place, the Tower gives such modifier instructions as a result of the perception of an arising risk. Maybe be an airplane landing behind you, could be an airplane likely to cross your likely exit, or worse, your mandatory RWY exit. It could be an understanding between Controllers and Pilots at a local  for convenience rather than purely Safety. You may not be aware of this last, depending on your experience, familiarity with the airfield and local procedures and conventions.
A few points come up:

in case of a readback/switchover situation, logic dictates that you need to give it a reasonable time on frequency, incase your readback has to be corrected, before switching frequencies. We get rushed sometimes due to a clash of procedures ("change to GND point Niner for further") and we are unable or it is impossible to prioritize.

Conversely when you change over frequency, good R/T practice requires a small pause before using the ptt to ensure you don't 'step  on' someone else's transmission (Who knows, could be a readback or it's acknowledgement).

an error, though it may not be a violation, may still need discussion, so as to come up with an understanding of what happened, why it happened and how we can help avoiding or eliminate  such occurrences.

As Pilot in Command, certain Controller instructions may not be acceptable to you. You may exercise your command authority, for the safety of the airplane, persons affected, and goods and property etc., but remember, you invariably must be able to defend your actions and decisions as being the safest course of action based on the info available to you and the realtime situation.

Seems Tower did the needful by contacting you via Ground freq. We pilots tend to (naturally) obsess about such occurrences, and the bogie of violations and consequences come more readily to mind, somewhat repressing a genuine concern for addressing the circumstances.

BTW, what did the Tower guys have to say to you in the end?

Do you have anything to backup up what "you'd say" for bullet point 1? That would help a lot, since you seem to be implying that this is regulatory.

Please see the current edit where I've added an extract (Para 5.2.9.2.2) from the ICAO Annexe 10 on "Aeronautical Telecommunications"

That does help. Unfortunately, an image is not searchable text for others who may be looking to refer to it. If you'll take the [tour] and read through the [help], you'll start to learn the standards that are expected of answers here. I'm not trying to pick on you, just take what seems to be a good answer and help it meet the expected standards here. I've noted, too, that you've answered several other questions - sharing your knowledege in a way that best helps the community benefits all.


text:
Why was the TSR-2 literally burnt down even before its first official flight?
The BAC TSR-2 was one of the aviation marvels of the time and the test flights had pretty good records. So why was it cancelled?

Yes, It was burnt down by the same people who built it.

I don't see what Wikipedia does not cover in this aspect.

The TSR-2 flew quite a few times (24 times); atleast the first prototype did. The mockup was burnt, not the prototype- one of them was shot to pieces for target practice, so pretty much the same fate.

The main reason cited for the cancellation was costs- the rising costs (quite common in new aircraft development), with the expected unit cost triple of original estimates led to the cancellation of the (behind schedule) aircraft by the cash strapped UK govt. The projected replacement, F-111 was also cancelled for the same reason. Note that TSR 2 was the last time the British went solo on combat aircraft development (with the exception of Harrier)- the amount of money required was simply more than what was available.
Strictly speaking, the test flights were not flawless - there were engine and landing gear problems, though these were typical in aircraft development. Though these were not insurmountable, the test flights were fairly typical of aircraft development and nothing special.
The test aircraft was not fitted with the full avionics package; so there is no way measure its performance. However, the entire system was new and would've caused issues with integration and performance (though in all fairness, there was no indication that that would be a great problem), not to mention the effect on cost.
Quite a few of the components developed for the aircraft (The engines, for example) were later used in other aircraft projects, so the program wasn't a total loss.

To a certain extent, development, manufacture and operation of new aircraft requires political will more than technical capability (which can be obtained, given enough time and money); the British govt. didn't have it.

"All modern aircraft have four dimensions: span, length, height and politics. TSR-2 got just the first three right ..." said Sir Sydney Camm.


text:
Which is the most efficient wing form in terms of performance and efficiency?
I am unable to decide as various forms have some or other advantages.

For high speed, high altitude?  For STOL?  For what application?

There's no way to answer this question unless you can make it more specific. As you said yourself, different designs have different advantages and disadvantages. If you can explain the aircraft type and how it will be used then you might get a better response.

Horizontal. Yes, a horizontal wing form is best.

I suspect this is for a RC model.

@PeterKämpf, but vertical wings are so much more exciting!

You will never find the answer. What is the best car design in performance and efficiency?
A truck is highly efficient (compared to a normal car) when transporting cargo, a jeep will be highly efficient on terrain (compared to a normal car that won't move at all...)
But two simple rules:

the more V-shaped, the better for high velocity
the larger, the better for low velocity


text:
Is there really anything to be gained by placing the propeller at the top of the vertical stabiliser?
I am currently designing an electrically powered RC plane with one propeller. The wingspan is c. 2.5 m and the length c. 1.6 m.
Right now the plan is to put the propeller at the top of the VS where the HS is also situated. However, as I've advanced further with my design, it has become clear that it is hard in all possible ways, starting from the structural traits (foam covered with fibreglass) to fitting the 40 mm engine along with the elevator servos.
So, should I just move the propeller + engine down to the aft of the fuselage or is there something about the performance that this move might adversely affect?
E: As mentioned in the comments, moving the motor would affect the pitching moment characteristics of the A/C. "Luckily" I have the option of changing the battery placement within the fuselage to counter this effect so the pitching moment consideration is made void by this.

The direction of the torque moment will be reversed, from nose up pitching to nose down pitching, affecting the stability, and requiring adjustments to balance this change.

Good question -- the Trislander's center engine got shoved exactly where you're talking about (i.e. top of the VS), so it's not completely unheard-of to do...

To place a heavy mass, part of which is even rotating, on a long, flexible beam is generally not a good idea. The engine mass will reduce the eigenfrequency of the vertical tail, inviting early flutter, and any imbalance in the propeller will provide the initial excitation which flutter needs to develop. Also, placing heavy masses away from the center of gravity increases the moments of inertia and makes the handling of the aircraft needlessly sluggish. The designers must feel some pain to pick this unattractive engine position.
Reasons for this unusual engine placement could be:

Better aerodynamic control for ground handling. With the control surfaces squat in the propeller's slipstream, ground handling of seaplanes on water is much improved.
Better visibility for the pilot: Instead of a center engine placement in the nose, a tail location gives much improved visibility.
Less FOD (foreign object damage): The raised prop position makes it less susceptible to being damaged by debris kicked up from the ground.

The first reason explains why most designs with tail-mounted engines are seaplanes. The engine location on the Trislander, the three-engined version of the Britten-Norman Islander, was picked for the last two reasons and because the designers felt that flutter was not much of an issue with that compact, slow utility aircraft.

I can find two examples of aircraft (Yes, using that term loosely) with a propeller engine mounted at the top of the vertical stabilizer:

Britten-Norman Trislander
A-90 Orlyonok

In both cases, this design is chosen due to the conditions where the craft will be operating.  The Trislander is designed for short take-off and landing on unprepared surfaces (island hopping is referenced in the name).  The Orlyonok is designed to operate in ground effect, which is even more of an "unprepared surface."  Engines and propellers far from the ground is a desired design trait in either case.
You don't mention if the propeller is in front of or behind the stabilizer.  I would think (IANAA*) that the propeller in front of the stabilizer would make the control surface less effective due to the disturbance of the propeller.  The control surfaces on both examples above seem oversized, which I will take as definitive proof of my hypothesis.
*I am not an aerodynamicist.

IANAA but I would have thought that the wind created by the propeller would make the control surfaces more efficient (greater airspeed)

There is even a third one: The Seawind seaplane

Another pair: the Stuttgart e-genius  and Icaré 2.

@ManuH I would argue this airflow would be more turbulent due to the propeller. I'm sure this effect is variable based on air speed. I honestly don't know.

authors: ธรรศธรรม พงศ์ศรีเพียร


text:
Are there any accident reports that mention hacked/compromised avionics as a factor?
Does anyone know of any documented examples of airline accidents caused by hacked or otherwise deliberately compromised avionics?

It may be more instructive to also ask "What preventative measures are in place to mitigate hacked or compromised avionics" since many of the answers include "There are no obvious incidents, and I wouldn't expect any because XYZ."

Searching the NTSB Accident Database which also covers some international commercial flights for the key words "hack", "hacked" do not provide any results related to hacked avionics. Likewise using the keyword "tampered" does not provide any results related to deliberate tampering with avionics (mostly "tampered" wreckage).
There is one individual, Chris Roberts, who claims to have hacked into the In-Flight Entertainment System (IFE) to cause the aircraft to deviate from its course, however I find it highly suspicious. From a security perspective, I can't of any good reason to have the IFE network on the same network as any avionics, however that isn't to say that there isn't some possible connection. The FBI certainly didn't think it was very funny.
So as of today there have not been any aviation accidents that are attributed to hacked or deliberately tampered-with avionics as a cause of said accident. The closest thing I think you will find is pilots loading incorrect flight plans, outdated (or even pre-dated) navigation data, and other cases of pilots not correctly using the equipment.

I did read your original question and would like to clarify. Conspiracy theories, guesses, and internet speculation are not a replacement for hard evidence. In the case of MH-17 the wreckage was recovered and no evidence has been presented in the favor of hacking, while there is a lot of evidence of the shoot-down. Airliners even at cruising altitude can be shot down by surface to air missiles rather easily.
As for MH-370, until the wreckage is found we may never know (and even if it is we may never know). Black boxes do not have an indefinite life span especially if they are under water. Until then theories of that flight being hacked are just as credible as those saying aliens abducted the entire flight and they are living on Neptune in specially constructed Igloos.

"I can't think of any good reason to have the IFE network on the same network as any avionics."  Unfortunately, there are bad reasons to have the IFE network on the same network as avionics (not that I know that's been done, I'm just saying.  For example, I can't think of any good reason why a car's entertainment system is on the same network as the engine controller/braking system, but we know that's done.)

The IFE needs to at least read the flight data, since it is displaying them. So it is up to the bridge to isolate it the other way and there can be a bug in it. @davidbak, in car, the “entertainment” system is also configuration system for many things, which is why it needs connection to the main bus and it must be two-way in that case. In the IFE case the data flow can at least be restricted to one-way.

I think the FBI reaction was stupid. They should have got the plane in question for a couple of hours and ask him to demonstrate it during ground run. If it succeeded, then he just raised valid concern, so should be thanked and FAA should enforce fixing it. Only if he failed, then it would be correct to charge him — with spreading panic.

@JanHudec - In the car case, the ent/nav system doesn't have to be on the bus, where it can read/write to any device.  There could be a point-to-point connection to a specialized controller that isolates (filters) the ent/nav system from the vehicle control systems.  And the same for the IFE system too: There could be an output-only stream (separate from any bus/network, and output-only based on the electronics it is built of) from the flight network to the IFE network (for all I know, that's the way its done).

@davidbak, well, the one car ent/nav system I have a bit of experience with was composed of two units, one running the user interface and nav and the other running the back-end (which included radio there). IIRC only the back-end was connected to CAN, the two boards had ethernet between them. So it was somewhat as you say. Still, CAN is a two-way bus, so if the back-end board is compromised, controllers can be accessed. However ARINC 429 is one-way (one-to-many), which should make it harder to break.

The problem is not to have things connected or not (they are), but how security is enforced using credentials. In the new era of virtualization virtual LANs are physically connected, but logically segmented. Did you know that your Intel CPU can access a network and exchange data when the laptop is powered off?

@mins True, however consider the implications of connecting cabin accessible equipment to the avionics vs adding a GPS for the flight path following, I still can't imagine a good reason for them to be physically connected, even if segregated.

@JanHudec I don't feel the same way about the FBI reaction. If he can't reproduce, its a threat (try running through the airport yelling "bomb" once, even if you don't have one). If he can, then he's compromising the safety of others (what if he locked the pilots out somehow and they crashed?). Just because you can do something but never intended to do damage doesn't mean it isn't illegal. If he wanted to demonstrate this, he should have brought it to the FBI's attention before attempting to do it on an active flight, or 15 as he said.

As @JanHudec mentioned, when using industrial serial buses (CAN, SDI, ...) manufacturers are not really worried about connecting everything to the same wire, and often modern security concepts have yet to spread within the engineering dept. I do believe avionics manufacturers are more concerned, but not sure how much more. The FA call button is connected to the FA system, connected to the audio panel, connected to the VOR, connected to the GPS, connected to the ACARS, etc.

"I can't think of any good reasons to connect it to the passenger network" isn't the same as "There are no good reasons", which itself isn't the same as "It's not connected to the passenger network".  I think you're writing from a position of ignorance here.  For example, despite @davidbak's comment, there are good reasons why the entertainment system in cars is connected to the engine controller system: when you drive faster, your car stereo's volume automatically increases.  You might not consider that good judgement, but that connection does exist, in cars.

Similarly, for airplanes, my understanding is that in some modern airplanes, the two networks are connected. The connections are supposed to have firewalls and logical segmentation that are hopefully adequate to prevent risks, but it's hard to say for sure that this is the case, based solely on public information -- there just doesn't seem to be enough information publicly available to say for sure.  I'm not an expert on this and I can't make authoritative statements about it... but it seems you might not be either. I'd suggest removing that part of the commentary in your answer.

@D.W. Actually, if that (audio volume increase) was a reason used to justify putting the entertainment system on the same bus as the engine controller I would call that a bad reason.  (I was not objecting to connections, just being on the same network (or bus). You could reach a safer design by having the engine controller broadcast, via some transmit-only mechanism, the desired telemetrics.)

@davidbak, that's fine.  As I already wrote, you might not consider it good judgement... but as I said, they are connected.  The fact that you think there's no good reason to connect them does not imply they are in fact disconnected.

@D.W. I said I can't think of a good reason for it to be, not that it isn't connected. I wasn't trying to imply that the systems are not connected, only that it isn't a good idea to have a system, especially with accessible ports in the passenger cabin, connected to critical flight controls.

I know.  What I said is, I suspect you're writing from a position of ignorance.  (I hope you won't take this personally.)  I think the fact that you can't think of a good reason isn't really relevant here to the question that actually matters: which is, are they in fact connected?  A statement that you can't think of a good reason for them to be connected unavoidably risks lending the impression that you intend for readers to infer that they probably aren't connected.  I think your answer would be improved by removing that statement.  Anyway, I've made my case; from here it's up to you.

@D.W. Part of my job is ensuring the security of control systems, systems that would have major consequences if compromised. I've written papers on industrial security and securing control systems from penetration and internal attacks, so I'm not exactly writing from a position of ignorance. Designing interconnected control systems is what I've been doing for a living for the past 15+ years.

Not ignorance about computer security in general or in industrial systems specifically... but rather, ignorance about the very specific question of whether the avionics networks are or aren't connected to passenger entertainment networks in any passenger airplane in current service.  See also my comments on the other answer for some links that might indicate why I'm raising this point.  (I'll also say that I've upvoted your answer and I find it helpful.  I am just suggesting one minor point on which I think it could be improved.)

An example a what is usual in industry: "In an aircraft network, there will be lots of systems connected in network. They will be synchronizing their time  with GPS. It  will be costly to  implement GPS receivers in each systems in the network. So, in an aircraft mainly central system will be getting its time from GPS. Other systems connected to central system will have to synchronize their time with the central system." (source). First "good" reason: cost! I'm not saying this will be done, just wanted to illustrate the mindset.

Related: Networked Local Area Networks in Aircraft: Safety, Security, and Certification Issues, and Initial Acceptance Criteria /// and /// Fly-By-Wireless for Next Generation Aircraft: Challenges and Potential solutions

No.  Near as I know, current navigation and flight control avionics are separate from internet connected components, so 'hacking' them is physically impossible.
Now, more types of cockpit avionics are becoming Bluetooth compatible, allowing for interconnectivity with internet connected mobile devices or apps eg Garmin Pilot, ForeFlight, etc., allowing a person to download a flight plan into a GNSS head for example.  Maybe some hacker at some point will analyze a security flaw within these avionics and be able to exploit this.
In addition, these systems often take software updates in the form of SD cards, USB thumb drives, etc. so there is a possibility of introducing malware into the system that way as well.
But even if a GPS head were attacked that way, there would be no means for it to gain access to the control systems of the a/c, the system could be manually shut down, and backup means of navigation used.
But in the era of Stuxnet and budding developments of cyber weaponry paralleling the development of the Internet of things, anything may be possible in the future; just not now.

"Near as I know, current navigation and flight control avionics are separate from internet connected components, so 'hacking' them is physically impossible." Hacking doesn't require the internet, just physical access. Also, Stuxnet is specific to Siemens PLC control systems (I'm a controls engineer) which really doesn't have a parallel in avionics...

"Near as I know, current navigation and flight control avionics are separate from internet connected components" - This does not appear to be accurate.  See, e.g., https://www.wired.com/2015/04/hackers-commandeer-new-planes-passenger-wi-fi/, which states that in some modern jets, the flight control avionics are on the same network as passenger entertainment systems.  There are supposedly firewalls, and if those firewalls are free of bugs this might be adequate to prevent the risks... but that's different from saying they are separate networks, or that hacking is "physically impossible".

See also https://www.schneier.com/blog/archives/2008/01/hacking_the_boe.html and http://www.dailytech.com/Boeing+787+Network+Vulnerability+Reports+Misleading/article10251.htm.  My guess/speculation is that many of the press articles are probably massively over-hyping the risk... but at the same time, the risk can't be completely discounted, and that statements that hacking is "physically impossible" are irresponsible and can't be justified based on the publicly available evidence.

That Wired article and the Schneider blog are tantamount to carnival barking.  Having worked on these kinds of aircraft, cockpit systems, flight controls, and IFEs, I can tell you there is no hard connection between critical avionics such as the flight control computers, air data computers, radios, nav heads, AFCS, auto throttles, etc., and satellite based WiFi networks.  No, as of today it is virtually impossible for a person working remotely to commandeer an aircraft by hacking into a IFE network.


text:
What is the process for converting a US certificate to a Japanese license?
I have a Japanese exchange student (here for at least 4 years) who is looking to pursue a pilot's certificate (up through commercial, potentially to an ATP rating) in the US and, upon returning to Japan, convert it into Japanese ratings and licenses and try to get into the airlines.
I'm trying to give him an idea of how difficult or not it is to make that happen, and what hoops he might need to jump through.  Google has only led me to outdated forums and websites, so I thought I'd give it a go here.
How do you convert a given US pilot's certificate (private pilot, commercial, ATP and ratings including instrument, etc.) to a Japanese license?

This page may be helpful from AOPA Japan: http://www.aopa.jp/Newenglish/Newenglish/Fly_1%20rev%202.html


text:
Why does the local speed of sound decrease with temperature and not pressure?
I presume I'm missing something here but from looking at charts indicating the value of Mach 1 at different altitudes it seemed to reduce the higher in the atmosphere you went which I presume is related to reduced temperature and not pressure related which to me seemed counter intuitive. Thanks, hopefully you can clear this up

While there are people who understand physics well around here, it would probably make more sense to ask this over on physics.

Sound speed depends both on pressure and density which cancel each other in an ideal gas ($c=\sqrt{\gamma \frac{p}{\rho} } $). But actually pressure has a small impact on real air. See Wikipedia.

It may be helpful to remember the ideal gas law here: $PV=Nk_BT$ (the physics version). If we divide both sides by $N$ we have a $V/N$ on the left which is just a $1/\rho$ where $\rho$ is the number density. Thus:
$\frac{P}{\rho}=k_BT$
In an ideal gas, to which air is close enough, the speed of sound is given by:
$c_s = \sqrt{\gamma \frac{P}{\rho}}$
Throwing in our first results, we see that:
$c_s = \sqrt{\gamma \frac{P}{\rho}} = \sqrt{\gamma k_BT}$
In other words, the speed of sound reduces with either pressure or temperature because those two are in turn connected by the ideal gas law. It's basically two different ways of looking at the same question.
Side note: throwing in the effect of density is another question all together since $c_s$ increases with an increase in temperature or pressure but decreases with an increase in density. The question then becomes whether the decrease due to the drop in pressure overcomes the increase due to the drop in density at higher altitude.

The side note is quite relevant. You show that speed of sound is a constant times temperature, but without knowing more about how pressure varies with density, it cannot be stated that speed of sound is a function of pressure.


text:
Why does the wing root of the A330 have a pronounced twist?
just wondering what the purpose of the pronounced twist on the Airbus A330 wing root is,  I've noticed this on the 380 as well.

What do you mean with twist on the wing root? The wing is twisted along its span to improve stall behaviour; that is used on all swept wings. But mentioning wing roots specifically suggests you might mean something else.

He/she probably used the term incorrectly; the twist in this case is most significant around the root, and is uniform along the rest of the wing rather than consistent across the whole section.

Short answer:
To create a funnel for all the air streaming towards the fuselage.
Slightly longer answer:
Air approaching a swept wing will be accelerated towards the area with the lowest pressure and, therefore, will be sucked towards the wing's center. The center itself will show a markedly different pressure distribution over chord than the two-dimensional flow over the same airfoil would because here the acceleration is much lower while the deceleration length at the end of the airfoil is compressed. If the swept wing has no twist and the same airfoil over span, a flow pattern similar to that pictured below will result:

The blue lines on the wing surface are lines of equal pressure (isobars) and in the plots denote the pressure coefficient on the upper side of the wing section. The red lines show the pressure coefficient on the lower side.
In order to maximize the achievable lift at transsonic speed it is desirable to modify this wing such that the isobars will run along lines of equal chord percentage over the full span. To achieve this, several tricks must be combined:

Make the root airfoil thicker at the front and thinner at the rear part.
Do the reverse for the tip airfoil: It must be made thinner at the front and thicker at the rear part.
Use negative camber at the wing root.
In order to compensate for the much higher zero-lift angle of attack of the modified root airfoil, increase its incidence.

The last step is what causes the kink in the trailing edge. Of course, increasing the wing chord at the center increases this effect. In case of the A330 and A340, the incidence changes from +4.5° at the root to 0° between 30% and 70% span and -2° at the tip when on the ground and -2° at 70% span and -5° at the tip in flight.
Thanks to @ymb1 who found a very illustrative picture of the A330 (shown below, source) the root twist becomes obvious: The root airfoil has visibly much less forward camber (negative camber, actually) and, consequently, a higher zero-lift angle. In order to produce a similar lift coefficient, the center wing needs a higher incidence to compensate for this change in airfoil shape.

Another find by @ymb1 is this picture of Airbus root airfoils (source). The thick nose is easy to spot; it is needed to shift the suction area on the swept wing root forward so that the pressure distribution becomes more similar to the one of the airfoil at mid-span. Also, while the top has a long straight stretch, the bottom is rounded which in combination produces negative camber. The rounded bottom helps to maximize relative thickness. Since the chord at the center wing is increased, the local lift coefficient can be smaller than on the mid and outer wing and still carry the same circulation for low induced drag. What is saved in lift is added in thickness for structural efficiency and for stowing the landing gear. The lack of rear loading (= high local camber in the rear airfoil section) helps to gain the needed volume for the landing gear bays.

Here is another one, this time an English Electric Lightning F.1. The reflections on the leading edge show nicely how it is pulled down at the root with plenty of nose camber there. This being a design from the early Fifties, this nose camber is used to give the wing better stall behavior and isobar shaping was not yet practised. Note that the local incidence has not been increased at the root.

EE Lightning F.1, Imperial War Museum, Duxford (Edited), CC BY-SA 2.0 (picture by Roland Turner from Birmingham, Great Britain; source)

@ymb1: Thank you for the contribution!

@PeterKämpf: question: what does blue and red line in your plot mean? I am really hoping blue line is the air speed, if that's the case the sudden drop in the blue line suggest the sudden drop in speed and sudden increase in pressure, that's where the normal shock wave and separation will be. I REALLY need some confirmation on this

@eliu: You are right, I should had explained that. Red is the lower side pressure coefficient and blue the upper side pressure coefficient. For pressure coefficient please read this answer.

@PeterKämpf: darn it... I was REALLY hoping the blue line was speed. That would have solved so much of my confusioning... Now, back to square one.
Can I assume that speed would roughly follow a similar curve to the blue?

@eliu No, not back to square one. The pressure coefficient is inversely proportional to the square of speed. Note the inverse y axis: A rising line means accelerated flow.

@PeterKämpf: This is my eureka moment! Thank you.

@PeterKämpf this was a great read, I know it's been a while but thank you for posting this! If you ever get to it, I would have loved to see the picture of the isobars and pressure distributions "after" the modifications.